Abstracts

Rationale: Beyond seizures, cognitive and psychiatric co-morbidity of patients have a major impact on their quality of life. Seizures and interictal epileptic discharge (IED) interfere with cognitive networks in an acute manner. Whether IED has a genuine role in chronic neuropsychological dysfunction is currently a matter of debate. Here we intended to probe the impact of IED on presurgical neuropsychological function, cognitive post-operative outcome and brain atrophy. Methods: Thirty-four patients with temporal lobe epilepsy and unilateral hippocampal sclerosis (right 17, left 17) were examined with 24-hour scalp-EEG, neuropsychological testing and MRI segmented with FreeSurfer. Interictal epileptique activity (IED), defined as spikes, sharp waves and sharp slow waves, was quantified per hour of wake and sleep EEG. Half of the patients had infrequent IED, i.e., less than 10 per hour, the other half frequent IED (more than 10/h). A large battery of neuropsychological testing included verbal and non-verbal memory, executive function and IQ. Patients were tested before and approximately 8 months after respective surgery. Most of the 24 patients who went on to epilepsy surgery became seizure free (68% Engel Class I). Results: Patients with more than 10 SW/h performed worse in nearly all realms of neuropsychological functioning. Their task scores were lower for IQ, for verbal and non verbal memory, for verbal and graphical fluency. Most significant results were obtained for IQ and executive function (z score group difference > 1,96; p < 0.05). IEDs contralateral to lesion were negatively correlated with global brain volume. Neither patients with low nor with high IED-rate improved with surgery, post-surgical neuropsychological results remained essentially stable. Hence, patients with high IED-rate did not show a particular benefit of surgery. Conclusions: IED is a biomarker of cognitive comorbidity and seems to be linked to brain atrophy. Successful surgery with remission of IEDs did not entail recovery of cognitive functions. Thus, IEDs do not seem to be a treatable cause of cognitive impairment, but rather an expression of the underlying structural disease. Funding: No funding